server.createContainerPlatform: fix userns + spoofed infra
server.createContainerPlatform: fix userns + spoofed infra

In case we spoof the infra container, its spec is nil and
if userns is enabled we get nil deref trying to read container's
mounts.

Skip this part for a spoofed infra container.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

kubernetes-incubator/cri-o,kubernetes-incubator/ocid,nalind/cri-o,kubernetes-incubator/ocid,kubernetes-incubator/cri-o,nalind/cri-o,nalind/cri-o,kubernetes-incubator/cri-o,kubernetes-incubator/ocid,kubernetes-incubator/cri-o